This invention relates to video display support mechanisms, specifically an improved position adjustable support for flat panel Liquid Crystal Displays (LCD), A worker at a typical computer terminal may be required to spend long hours in a somewhat constrained physical posture. In order to maintain user comfort and create the proper ergonomic position of the video display it is often necessary for the user to be able to adjust the position of his video display. Various prior art mechanisms have created devices that give the user this adjustability, however, these previous designs have inherent mechanical and functional shortcomings.
The typical prior art mounting systems contain various combinations of mounting brackets, support arms, friction locking knobs, ball gimbals, arcuate slots, mechanical springs, and gas springs. While the majority of these designs solve several of the typical usage problems, they are not very efficient support mechanism throughout their limited range of motion.
Typical single arm models such as described in prior art (U.S. Pat. No. 4,768,744 to Leeds) have their support arm pivot axis mounted in a low position near the users work surface. This has the effect of limiting the vertical adjustably range that the user might need. This is very important in a situation where the user has other furniture such as a keyboard support that has the ability to adjust to a standing height position. Due to this restriction this type of support mechanism is usually limited to supporting larger heavier CRT type displays.
A second typical prior art design (U.S. Pat. No. 6,019,332 to Sweere) incorporates a gas spring whose stored energy is used to counter balance the forces generated by the display. In this and numerous other existing devices the gas spring is mounted in a position such that its axis is at a relatively small distance from the pivot axis of the support arm and the angle to the axis of the support arm is relatively small. In these types of mechanisms the close proximity of the gas spring axis to the pivot axis of the arm requires the gas spring to exert very high forces to counter balance the weight of a typical display. These forces are in the range of 400-800 Newtons (N). These high forces limit the materials that can be used in the design of the highly stressed supporting components to various types of metals.
In order to calibrate this type of mechanism initially to provide the proper counter balance for the display, the user must adjust a bolt or screw with some type of tool such as a wrench or screw driver. This adjustment is generally difficult to accomplish due to the previously described high forces generated by the gas spring. This adjustment increases (or decreases) the distance from the axis of the gas spring to the pivot point of the arm, therefore increasing (or decreasing) the counter balance moment generated by the spring.
Since the distance from the axis of the gas spring to the axis of the arm pivot is relatively small, and the adjustment mechanism typically does not increase this distance significantly, the ratio of the heaviest loads that can be counter balanced to the lightest loads possible rarely exceeds 2 to 1. This can require that the user determine the weight of his display, and purchase a support mechanism with the correspondingly correct range of adjustability. This is evidenced in several existing products that are required to offer several models with different load range capabilities.
The design of the mechanisms that have the gas spring mounted generally parallel to the arm have an additional short coming in that the user is instructed to calibrate the counter balance while the support arm is in a horizontal position. It can be seen that through the range of articulation, the counter balancing force generated by the gas spring not only changes in magnitude, but also in direction. These changes produce a counter balancing moment that is continuously varying, with respect to the angle of the arm position and the internal characteristics of the gas spring. At the same time the moment generated by the load varies with the angle of the supporting arm. Trying to equate these two moments, as is necessary for a truly balanced condition, is very difficult, if not impossible. Since the counter balancing moments do not necessarily closely match the moments generated by the load, the load will tend to fade from the highest position toward the previously balanced horizontal position. Likewise, when the load is in the lowest position, it may be over balanced by the gas spring forces and it will tend to rise towards the horizontal position. In order to over come this inherent problem, many designs incorporate springs and polymer washers to increase the friction in the pivot areas. This in turn requires the user to apply much more force to reposition the load, because he must overcome the sum of the gas spring forces and the additional friction forces. These types of mechanisms do however operate adequately in a small range of motion.
In the previously mentioned prior art (Sweere), a second, manual adjustment in incorporated. This adjustment overcomes the small range of motion problem by allowing the user to access a more coarse adjustment through the use of a toothed ratchet mechanism. This in effect limits the counter balancing requirement placed on the gas spring to a smaller range of stroke.